Subj : Re: Challenge: Multithreading & Synchronization
To   : comp.programming.threads
From : Uenal Mutlu
Date : Sat May 21 2005 12:32 am

"Maciej Sobczak" wrote
> Uenal Mutlu wrote:
>
> >>print("I'm doing something");
> >>
> >>Show me how you make it lockable. Forget about streams, cout, stdout or
> >>any other object.
> >
> > If you cannot assign a mutex to an object (funny imagination in MT app, btw)
> > then use a wrapper + mutex for it. Like this one:
> > mutex gm;
> > void myprint(char* Apsz)
> > {
> >   Locker L(gm);
> >   print(Apsz);
> > }
>
> Cool.
>
> void f1()
> {
>      myprint("First name : Maciej");
>      myprint("Family name: Sobczak");
>      myprint("Profession : Programmer");
> }
>
> void f2()
> {
>      myprint("First name : Cody");
>      myprint("Family name: Hacker");
>      myprint("Profession : Programmer");
> }
>
> No luck, sorry. I run f1 and f2 in two threads and I got this:
>
> First name : Cody
> First name : Maciej
> Family name: Sobczak
> Profession : Programmer
> Family name: Hacker
> Profession : Programmer

Simple solution: Add this at top of your two functions f1() and f2():
      Locker L(gm);
And leave myprint() as currently is.
But, your mutex must be of recursive type.

> How do you achieve the "wait for something to be done"?
>
> Example:
> One thread moves some elements from one container to another. I want to
> know (in different thread) when it is done.

I personally do use an atomic flag (actually it is an atomic counter with the
possible values 0 and 1). I've this implemented in a class. Internally it uses
InterLockedXXX funcs of the Win32 API.
There are many alternatives. The simplest is:
   volatile bool gMyFlag = false;
BUT: this method is not recommended.

.